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Project Introduction

Chromologic (CL) and the California Institute of Technology (Caltech) propose to continue the Phase II STTR development and demonstration of a Multifunctional Environmental Digital Scanning Electron Microprobe (MEDSEM) instrument that transmits high energy beams of electrons sequentially using a two-dimensional array of multiple, miniaturized electron probes into a planetary atmosphere and strike solid or liquid planetary surfaces to simultaneously generate a wealth of spatially-mapped compositional information. MEDSEM will ultimately simultaneously measure X-ray Fluorescence (XRF), Backscattered Electron (BSE) Spectra, Optical Spectra (OS) and Mass Spectra (MS). During the Phase II project Caltech will build on its transfer of electron-transmissive membrane technologies (Phase I) and further transfer to CL the technology for building an array of miniaturized, high-energy electron optic columns (EOCs) that are encapsulated by the microfabricated, electron-transmissive membranes for exciting XRF from samples in an atmospheric ambient. Electron field-emitter sources for these columns will be procured by Caltech from Stellarray Inc. and integrated with the high-energy electron columns. CL will manage the overall STTR Phase 2 project and assist Caltech in the fabrication and integration of EOCs, perform electron-optical and XRF-generation computer simulations to optimize the MEDSEM design, lead the testing and characterization of the Phase II MEDSEM prototype, and ultimately demonstrate the MEDSEM prototype performance. The 24-month Phase II effort will be aimed at developing and demonstrating a prototype MEDSEM prototype instrument (TRL6). The MEDSEM prototype will be capable of generating high-energy electron beams (10-30 keV), transmitting them into the atmospheric ambient and generating characteristic XRF from suitable planetary mineral sample analogs.
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Anticipated Benefits

MEDSEM satisfies NASA?s stated need for new and innovative scientific measurements for in situ planetary exploration. To date, although miniaturizing scanning electron microscopes has been a ?holy grail? for developers of planetary instruments, an in situ electron microprobe instrument has never flown. Once successfully demonstrated, MEDSEM would be a strong candidate for planetary instrument payloads for NASA?s future landed missions, as described by the National Research Council Committee on the Planetary Science Decadal Survey for future NASA missions from 2013 ? 2022. According to the Decadal Survey, primary planetary targets for landed missions include the moon, Mars, Venus and Europa. MEDSEM offers the great promise of offering multiple, orthogonal sensing measurements (XRF, BSE, Cathodoluminescence, and Mass spectrometry) all within a single instrument thereby drastically reducing the Size, Weight and Power (SWaP) required for flying each of these measurement modalities as separate mission instruments.

In the fields of materials science and engineering, geology, oil exploration, scrap and precious metals identification, academic research outside of NASA, there is a great need for capable, field-portable instruments that are rugged and reliable. As with NASA missions, size, weight and power consumption are of concern for humans transporting these instruments into remote locations for geological studies, environmental monitoring and oil exploration. An added concern is the overall cost of the instrument, especially for widespread acceptance and use. A successful MEDSEM instrument would also open up numerous applications in the educational arena. At both the K-12 and college level, MEDSEM could be used for science demonstrations as well as for hands-on experimentation and research in chemistry, solid-state physics, geology and materials science laboratories. Although MEDSEM cannot match the spatial resolution of terrestrial laboratory instruments such as scanning electron microscopes (mm vs nm), still it could serve as a rapid screening device with the ability to answer basic composition-related questions. MEDSEM?s primary advantage, of course, is its ability to simultaneously make multiple, different measurements on the samples being studied in ordinary room air. It is anticipated that MEDSEM will continue to evolve as an instrument, incorporating the latest advancements in micro- and nanotechnology.
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